The present invention relates to the field of electronic modules, and, more particularly, to electronic modules including a substrate for cooling one or more electronic devices and associated methods.
Electronic devices are widely used in many types of electronic equipment. One electronic device is the integrated circuit which may include a silicon or gallium arsenide substrate and a number of active devices, such as transistors, etc. formed in an upper surface of the substrate. It is also typically required to support one or more such integrated circuits in a package that provides protection and permits external electrical connection.
As the density of active devices on typical integrated circuits has increased, dissipation of the heat generated has become increasingly more important. In particular, a relatively large amount of heat may be generated in multi-chip modules (MCMs), microwave transmitters, and photonic devices, for example.
One device which has been used in a variety of applications, including electronic circuit modules, to provide high thermal transport over long distances is the so-called xe2x80x9cheat pipe.xe2x80x9d A heat pipe is a sealed system that includes an evaporator, a condenser, an adiabatic region connecting the evaporator and condenser for liquid and vapor transport, and a capillary or wick for circulating cooling fluid therein. Heat pipes enjoy an advantage over other forms of heat regulating devices in that they can transfer heat without the need for a mechanical pump, compressor or electronic controls, which may provide space savings in certain instances.
An example of an MCM which uses a heat pipe is disclosed in U.S. Pat. No. 5,216,580 to Davidson et al. entitled xe2x80x9cOptimized Integral Heat Pipe and Electronic Module Arrangement.xe2x80x9d This MCM includes electronic circuit components mounted on one side thereof and a thermal wick mounted on another side. A heat pipe evaporator and condenser assembly is attached to the MCM and wick assembly. Furthermore, a suitable working fluid is introduced into the heat pipe assembly which is then hermetically sealed.
Of course, cooling devices generally need to be on the same size scale as the electronic devices they are intended to cool. Yet, the benefits associated with heat pipes are subject to scaling limitations. That is, ever increasing packaging densities, which put high power devices in close proximity with conventional circuitry, may require that larger amounts of heat be transferred more quickly than is possible using conventional heat pipe assemblies not having a pump.
In view of the foregoing background, it is therefore an object of the invention to provide an electronic module and related methods which provides adequate cooling of one or more electronic devices and has relatively small dimensions.
This and other objects, features, and advantages in accordance with the present invention are provided by an electronic module including a cooling substrate, an electronic device mounted on the cooling substrate, and a heat sink adjacent the cooling substrate. The cooling substrate may include an evaporator chamber adjacent the electronic device, at least one condenser chamber adjacent the heat sink, and at least one cooling fluid passageway connecting the evaporator chamber in fluid communication with the at least one condenser chamber.
More particularly, the electronic module may include an evaporator thermal transfer body connected in thermal communication between the evaporator chamber and the electronic device. Additionally, at least one condenser thermal transfer body may also be connected in thermal communication between the at least one condenser chamber and the heat sink. The evaporator thermal transfer body and the at least one condenser thermal transfer body preferably have a higher thermal conductivity than adjacent cooling substrate portions. The thermal conductivities of the evaporator thermal transfer body and the at least one condenser thermal transfer body may be greater than about 100 Watts per meter-degree Celsius, for example. As such, the evaporator thermal transfer body, the at least one condenser thermal transfer body, and the at least one cooling fluid passageway may cause fluid flow during operation of the electronic module without a pump.
The evaporator thermal transfer body may include a wicking portion exposed within the evaporator chamber for facilitating cooling fluid flow by capillary action. Further, the wicking portion may include a plurality of projections, and the projections may be arranged in a generally rectangular pattern. Additionally, the evaporator thermal transfer body may further include a base plate carrying the wicking portion for facilitating sealing with adjacent cooling substrate portions. The fluid wicking portion may reduce the effects of pool boiling and extend an upper power density limit of the electronic device.
Furthermore, the at least one condenser thermal transfer body may include at least one wicking portion exposed within the at least one condenser chamber for facilitating cooling fluid flow by capillary action. The at least one condenser thermal transfer body may include a reservoir portion adjacent the at least one wicking portion defining a cooling fluid reservoir. Also, the at least one wicking portion may include at least one base and a plurality of projections extending outwardly therefrom.
The plurality of projections of the at least one condenser thermal transfer body may be arranged in two generally rectangular groups oriented at a substantially right angle. In addition, each of the projections may include a reduced width tip portion. The at least one condenser thermal transfer body may further include a base plate carrying the at least one wicking portion for facilitating sealing with adjacent cooling substrate portions. The at least one condenser thermal transfer body thus promotes clearing of condensate from a condensing surface thereof to provide substantially unimpeded condensation.
Additionally, the cooling substrate may further include projections extending inwardly into the at least one cooling fluid passageway for facilitating cooling fluid flow by capillary action. Likewise, the cooling substrate may include projections extending inwardly into the evaporator chamber and the at least one condenser chamber for facilitating cooling fluid flow by capillary action. More specifically, each of the evaporator and the at least one condenser thermal transfer bodies may include at least one of a copper-graphite composite, AlSiC, and metal, and the cooling substrate may include ceramic. The evaporator and the at least one condenser thermal transfer bodies are preferably resistant to corrosion from the cooling fluid.
A method aspect of the invention is for making an electronic module including forming a cooling substrate having an evaporator chamber, at least one condenser chamber, and at least one cooling fluid passageway connecting the evaporator chamber in fluid communication with the at least one condenser chamber. An electronic device is mounted on the cooling substrate adjacent the evaporator chamber. Further, an evaporator thermal transfer body is connected in thermal communication between the evaporator chamber and the electronic device. The evaporator thermal transfer body preferably has a higher thermal conductivity than adjacent cooling substrate portions. Also, a heat sink may be connected to the cooling substrate adjacent the at least one condenser chamber.
According to another method aspect of the present invention, a cooling substrate is formed having an evaporator chamber, at least one condenser chamber, and at least one cooling fluid passageway connecting the evaporator chamber in fluid communication with the at least one condenser chamber. An electronic device is mounted on the cooling substrate adjacent the evaporator chamber, and at least one condenser thermal transfer body is connected in thermal communication between the at least one condenser chamber. The at least one condenser thermal transfer body preferably has a higher thermal conductivity than adjacent cooling substrate portions. Also, a heat sink may be connected to the cooling substrate adjacent the at least one condenser chamber.